How to call a MATLAB Builder NE function with a struct as input

I have built a .NET dll with MATLAB Builder NE which has a funtion "MPCSolve". This function takes a struct "problem" as input. The struct contains vectors of different lengths. The output of the function are two structs and one scalar value. Compilation and add as reference in Visual Studio works. But I don't know how to construct the struct "problem" to call the function. How do I define this struct? I think it has to be a MWArray type.